If you look at the the green channel of the image, the information that you're interested in is somewhat contrasted against the background, by multiplying the channel with itself you increase the contrast, you can further increase the contrast by using a curves or levels adjustment.
Once you've created a channel with high enough contrast you can use it as a mask (by inverting it, crtl-clicking it, and clicking the 'add layer mask' button on the layers tab) on the original image, hiding the background and keeping the spots you're interested in.
You can also grow and shrink the mask using the minimum and maximum filters.
If your other images are in the same color range you can record and action and batch-run it on all of them.